"The Greek word for `cross' (Stau·ros´) means primarily an upright stake or beam, and secondarily a stake used as an instrument for punishment and execution." - Douglas' New Bible Dictionary of 1985 under "Cross," page 253. The word "Stau·ros´ in both the classical Greek and Koine carries no thought of a "cross" made of two timbers. It means only an upright stake, pale, pile, or pole.
But even if we ignore the evidence and assume that Jesus was killed on a cross, the most important thing is that the cross should not be venerated. Whether it was an upright single torture stake, a cross, an arrow, a lance, or a knife, should such an instrument really be used in worship?
Not only should the thought of venerating the very instrument of Jesus' execution be revolting in itself, but the symbol of the cross is also a pagan symbol...idolatry that God commands us to not even "touch":
"Do not become unevenly yoked with unbelievers. For what fellowship do righteousness and lawlessness have? . . . `Quit touching the unclean thing.'" (2 Corinthians 6:14, 17)
“Guard yourselves from idols.” (1 John 5:21)
“What agreement does God’s temple have with idols?” (2 Corinthians 6:16)
For more, see:
Did Jesus Really Die on a Cross? - What Does the Cross Symbolize?
Should Icons Be Used in Worship?